I observed a number of people say one thing in a group setting but would confess to other things off the record. The purse string issue was high for a lot of people, but as you say that wasn't the only motivation.
I think too that we oversold the Enlightened Self Interest value to the company in open sourcing internal tools. People worked hard on code that they didn't want to have to write again somewhere else, especially not several times. My current and future job satisfaction are elevated by convincing my bosses to free the code, the Greater Good is also improved by doing so. Nothing makes me want to leave like feeling trapped, and any work I do that has value past my expiration date is a big part of feeling like being here still is a choice.
But I think only a few companies ever enjoyed the fruits of that effort to the degree that we were all telling them they would. Sun Microsystems in particular. But the industry benefited enormously, so history will probably be fairly kind.
Even for commercial software, if it were easy to purchase, I'd still have to figure out how to make sure we comply with the licensing, get the key into the server, figure out how to deploy it (and not be able to inspect the software to see how it works if I need to).
Or I can just go to github, make sure it has an acceptable license, and run import-from-pypy foobar==1.0.
That license is worded specifically for me to use my private copy at work without exposing my employer to liability.
It's surprising to me that more organizations haven't followed suit. But many of these tools run either on the server or on a CI/CD machine so I'm not sure how you'd work that.
...and that we're stuck in a local minima where we now have to get over other, similar approval barriers to send money back towards open source projects? (in the case of projects that accept funding, at least)
(it's possible I've misinterpreted; and, for what it's worth, I think there are other reasons that FOSS has succeeded in addition to what you say - but I like that way of looking at the current landscape)